Oxidation of methyl mercaptan



N0V 4, 1958 J. N. HAlMsOHN ETAI. 2,859,249

OXIDATION oF METHYL `NIEMAPTAN Filed Jan. 17, 1957 19 J ma Hy A MEMBER 0F THE FIRM United States Patent O OXIDATION OF NIETHYL l\'1ERCAPTAN Jerome N. Haimsohn, Ardsley, Joseph T. Bashour, New York, and Joseph T. Rabatin, Nyack, N. Y., assignors to Staulfer Chemical Company, a corporation of Delaware Application January 17, 1957, Serial No. 634,791

6 claims. (C1. 26o-60s) This invention relates to a method of making ,organic disuldes and particularly lower `alkyl disulfides such yas dimethyl disulfide.

It is known that methyl mercaptan and an oxygencontaining gas such as air can be reacted by passing them over a solid catalyst to produce dimethyl disulfide. However, when such a process is used with a fixed bed catalyst, the resulting product contains, roughly, 75% of the desired dimethyl disulfide, about of low boiling by-products, and about 20% of high boiling byproducts. Such a reaction is ordinarily started by heating the solid catalyst to about 100 C. and passing the mercaptan-air mixture over the catalyst. The reaction is highly exothermic and the reaction rate is such that even at moderate space velocities, a localized hot spot of over 350 C. occurs at the point of first contact of the catalyst with the gas mixture. The excessive localized heat in the catalyst bed is a deleterious factor which results in excess by-product formation and also in decreased catalyst life. It has been found impossible' to control this localized heat by conventional heat transfer methods. v

Although the invention is described in terms of Vthe manufacture of dimethyl disulfide, it should be understood that the invention is applicable to any of the lower alkyl mercaptans having from 1 to 4 carbon atoms to produce corresponding disulides. Thus, methyl, ethyl, propyl and butyl mercaptans are suitable starting materials.

In accordance with the present invention, it has been found that by the use of a liuidized catalyst and by' controlling the temperature within certain relatively narrow limits, a yield of over 95% of dimethyl disulfide can be obtained with long catalyst life. In accordance with the present invention, the preferred operating temperature is about 200 C., but it may be as low as 170 C. or as high as 270 C. By operating under these conditions with a uidized catalyst, the organic product of the reaction contains a minimum of 95% dimethyly disulfide and over pounds of the desired product cany be made per pound of catalyst without any observable detrimental eifect on catalyst activity. Although it is possible to at least partially regenerate a catalyst by passing a steam-air mixture over the catalyst at an elevated temperature, the elimination of regeneration by uidization which permits selection of the optimum operating temperature is highly desirable as it reduces the expense of carrying out the synthesis. The use of a iluidized catalyst makes possible, when necessary, the removal of spent catalyst and the feeding of fresh or regenerated catalyst in a continuous manner, without interruption or shut-down of the process.

The drawing forming a part of this application comprises a schematic apparatus set-up and a flow sheet of a preferred method of carrying out the reaction of the present invention. In accordance with the flow sheet outlined, a hot Water bath 1 is used to maintain temperature, and thus pressure 'to force liquid mercaptan 2,859,249 Patented'Nov. 4, 1958 2 A "f from the cylinders 2. A control valve 3 is provided for controlling the ow of mercaptan to the vaporizer 4, where it is completely vaporized by heat'from a steam coil. 'Ihe volatilized mercaptan is`then passed through a mercaptan meter 5, while air from a compressor (not shown) is passed through -an air meter- 6, the ratio of the mercaptan to air being controlled by a ratio control meter 12. The mixture of mercaptan and air is then passed through line 7 to the reactor 9.y Line 7 also leads to a catalyst charging system 8 so that lfresh catalyst vor make-up catalyst can be introduced periodically into the reactor so' thata suitable amount'ofan appropriate catalyst'is present in the reactor. The reactor 9 is equipped with a jacket 10, which is provided with an inlet 13 and an outlet 11 for steam or other temperature control uid. The eluent from the Areactor 9 is passed through line 14 to a condenser 15, and the condensate is passed througha graduated receiver to the crude product receiver and decanter 16f The water which is formed by the reaction isseparated in the decanter 16 and is removedthrough line 17, while the organic product is taken through line'18 and filter 25 to the stripping column 19. 19, ,unreacted mercaptan is removed from the product and is passed through line 20 toV line 24, Where itgis combined with the non-condensible eiuent fromjcondenser 15, and is passed to the refrigerated condenser 21 and thus the recovered mercaptan is collected in the cylinders 22. The less volatile disullide is removed from the stripping column 19 as a bottoms throughY linei23,

and is sent to storage. Catalyst carried over from the reactor is collected in the tilter 25.

Various oxidation catalysts may be used as are Well known to those skilled in the artas. useful in promoting this reaction; these include thermally activated bauxite, activated charcoal, nickel oxide, iron oxide, copper oxide' and cobalt oxide; see Patents 2,028,303, 2,320,939 and 2,558,221 for suitable catalysts. The catalyst is employed in such iinely rdivided form and the feed rate' of the air-mercaptan stream is such that the catalyst is maintained in gaseous suspension in the reactor.J

As the oxidizing gas one can use oxygen, air or other4 oxidizing gases containing. freeV or combined oxygen, e. g. nitrogen oxides or hydrogen peroxide; see Patent 2,028,303.

The following non-limiting examples illustrate. preferred methods of carrying out the process of the present invention.

.Example 1.-A gaseous mixture containing airrand' methyl mercaptan in a 1.25 1.0 mole ratio (stoichiometrion oxygen) was passed into a reactorv containing a fluidized, nely divided thermally activated bauxite catalyst having a particle size range from to 200 mesh` at ai space rate of 22 cu. ft. per minute per cu. ft. of catalyst at a temperature of 1951-5 C. and at about atmos-fr The reaction chamber consisted of a"Y pheric pressure. l diameter column 31/2 ft. high with a 2 diameterv 3f highcooling jacket. Heated ethylene glycol was circulated through the reactor jacket, first to preheat thef catalyst charge, then to maintain the reaction tempera-1i ture at 195 C. The reaction chamber was` chargedV with 0.33 1b. of catalyst which resulted in ,a,"l2 static bed height. Under the operating conditions describe l the expanded catalyst bed height was 18".

In the stripping col-umn'V purityof 95% as determined by distillation.

dimethyl disulfide with hydrogen peroxide. The results were -as follows for the single pass air oxidation:

A[Basis 100 lbs. mercaptan input] I Lbs. Dimethyl disulfide l8.1 Unreacted MeSH 4 High boiler by-product 4 Mechanical loss 11 Example 2.-The gaseous mixture of Example 1 was reacted at a reaction temperature of 17o-175 C., all otherprocess variables being the same as in Example 1.

The overall results were `as follows for the single-pass air oxidation: Y

` Anjinitial conversion to dimethyl disulfide of 80% was obtained. The conversion gradually decreased to 75% 'when 13 pounds of dimethyl disulde per pound of catalyst had been produced; and continued to decrease to 70% when 18 pounds disullde per pound of catalyst had been produced. 'Ihis decrease in conversion rate was indicative of Vloss of catalyst activity which did not occur at the temperature employed in Example l.

Example 3.-'I'he process of Example l was repeated except that activated cocoanut` charcoal was used as the iuidiz'ed catalyst. The charcoalwas sized as -50-1-80 U. S. sieve. The reaction chamber was charged with 0.09 lb. of activated cocoanut charcoal which resulted in anv 8 inch static bed height. Under operating conditions the expandedY catalyst bed height was about 11 inches.

The gaseous mixture of air and methyl mercaptan in Ian 1.25: 1.0 mole` ratio (stoichiometric oxygen) was passed into the reactor at a space rate of 25 cu. ft. per min. per cu.'ft. of catalyst at a temperature of 196 C. :1:5o and at aboutatmospheric pressure.

k'The conversion of methyl mercaptan to dimethyl disulde was 71% in a single pass.

Example-*L The process of Example l was repeated except that the catalyst was nickel oxide supported on pumice. It was prepared as follows: A solution of 140 gms. nickelous nitrate hexahydrate in 200 ml. of water was slurried with 140 gms. of ground pumice. The slurry wasdried at 120-130 C., with intermittent mixing. K The dried solids were then fluidized in an air stream at a temperature of 600 C. for 4 hours to convert the nickel nitrate'to nickel oxide. The catalyst .as used contained 16.5% nickel, and was sized as -80-i-150 U. S. sieve.

The reaction chamber was charged with 0.17 lb. of catalyst which resulted in an 8 inch static bed height. Under operating conditions the expanded catalyst bed height was about 11 inches. A gaseous mixture of air andmethyl mercaptan in a 125:1.0 mole ratio (stoichiometric oxygen) was passed into the reactor at` a space rateof 25 cu. ft. per min. per cu. ft. of catalyst at a temperature of 205 C15 and at about atmospheric pressure.

disulfide was obtained in a single pass.

A 74% conversion of methyl mercaptan to dimethyll Example 5.-The process of Example l was repeated except that the catalyst was cobalt oxide supported onL pumice. It was prepared as follows: A solution of gms. of cobaltous nitrate hexahydrate in 200 ml. of water was slurried with 140 gms. of ground pumice. The slurry was dried at 1Z0-130 C. withV intermittent mixing.` The dried solids were then uidized in a ow of steam at a temperature of 316 C. for 3 hours to convert the cobalt nitrate to cobalt oxide. The catalyst as used cont tained 15.1% cobalt sieve. Y

The reaction chamber was charged with 0.17 lb. of catalyst which resulted in an 8 inch static bed height. Under operating conditions the expanded catalyst bed height was about 11 inches. A gaseous mixture of air and methyl mercaptan in a 1.25 :1.0 mole ratio (stoichiometric oxygen) was passed into the reactor at a space rate of 25 cu. ft. per min. per cu. ft. of catalyst at a temperature of 200 C.i5 and at about atmosphericl pres,-

sure.

The conversion of methyl mercaptan to dimethyl `disulde was 67% in a single pass.

Example 6.-The process of Example l was repeated except that the catalyst was iron oxide supported n pumice. It was prepared as follows: A solution of 140 gms. of ferrie nitrate nonahydrate in about 200 ml. ofV Water was slurried with 1'40 gms.v of ground pumice. The slurry was driedV at 1Z0-130 C. with intermittent mix-V ing. The dried solids were then iluidized in a flow of steam at 316 C. for 3 hours to convert the iron nitrate to iron oxide. The iron content of the catalyst as used was 11.8%. The catalyst was sized as -80-1-150 U. S.

sieve.

The reaction chamber Was charged with 0.17 lb. yof catalyst whichresulted in an 8 Ainch static bed height. Under operating conditions the expanded catalyst bed height was about 11 inches. A gaseous mixture of air and methyl mercaptan in 1.25 :1.0 mole ratio. (stoichiometric oxygen) was passed into the reactor at a space rate of 2.5 cu. ft. per min. per cu. ft. of catalyst at a temperature of C. *5 and at about atmospheric pressure.`

A 76% conversion of methyl rnercaptan to dimethyl disulfide was obtained in a single pass.

Example 7.-The process of Example 1 was repeated except that the catalyst was copper oxide supported on pumice. It was. prepared as follows: A solution of 140 gms. of cupric nitrate trihydrate in about 200 ml. of water was slurried with.140 gms. of ground pumice.l The slurry was dried at 1Z0-13.0 C. with intermittent mixing. The* dried solids were 'then fiuidized in an air stream at 400 C. for 4` hours to convert the copper nitrate to copper oxide. The copper content of the catalyst as used was 12.4%. The catalyst was sized as -80-|150 U. S. sieve.

The reaction chamber was charged with 0.17 1b. of catalyst which resulted in an 8 inch static bed height. Under operating. conditions the expanded catalyst bed height was about 1l inches. A gaseous mixture of air and methyl mercapt'an in 1.25 :1.0 mole ratio (stoichiometric oxygen) was passed into the reactor at a space rate of 25 cu. ft. per min. per cu.. ft. of catalyst at a temand was sized as 804-1150 U. S.

` perature of 197 C iS" and at about atmospheric pressure. Y

The conversion -of methyl mercaptanto dimethyl di# sulfide was 57% in a single pass.

This is a continuation-in-part of application Serial No. 499,310, led Aprilv 5, 1955.

We claim:

l. In a process for manufacture of lower alkyl disuldes from lower alkyl mercaptans by catalytic oxidation of vthe disuldes with a gas containing free oxygen, the improvement consisting in the steps of passing a vapork mixture of said mercaptans and gas -upwardly through a mass of nely divided catalyst for the oxidation of said mercaptans to said disulides .and at a rate in relation to said catalyst mass sufcient to maintain said nely divided catalyst in a fluidized condition in a reaction zone, maintaining said reaction zone at a temperature of from about 170 C. to vabout 270 C., and withdrawing an exit gas stream containing corresponding disuldes.

2. A process as in claim l wherein the mercaptan is methyl mercaptan.

3. A process as in claim 2 wherein the catalyst is thermally activated bauxite.

4. A process as in claim 3 wherein the gas containing available oxygen is -air and the methyl mercaptan to air molal ratio is about 1.2511 and the temperature is about 200 C.

5. A process for manufacture of a lower alkyl disulde from the corresponding lower alkyl mercaptan comprising maintaining a nely divided oxidation catalyst in uid suspension in a reaction zone, maintaining the tem- 6 perature of said zone between 170 and 270 C., and introducing a gaseous stream of a free oxygen containing gas and said lower alkyl mercaptan into the bottom of said zone to maintain said catalyst in gaseous suspension in said zone.

6. A continuous process for the manufacture of a lower alkyl disulide comprising suspending a finely divided oxidation catalyst in Ia gaseous stream of 'a lower alkylmercaptan and a free oxygen containing gas in a reaction zone, and maintaining said zone at a temperature of l70-270 C.

Mertz et al. June 26, 1951 Jewell Mar. 2, 1954 

1. IN A PROCESS FOR MANUFACTURE OF LOWER ALKYL DISULFIDES FROM LOWER ALKYL MERCAPTANS BY CATALYTIC OXIDATION OF THE DISULFIDES WITH A GAS CONTAINING FREE OXYGEN, THE IMPROVEMENT CONSISTING IN THE STEPS OF PASSING A VAPOR MIXTURE OF SAID MERCAPTANS AND GAS UPWARDLY THROUGH A MASS OF FINELY DIVIDED CATALYST FOR THE OXIDATION OF SAID MERCATANS TO SAID DISULFIDES AND AT A RATE IN RELATION TO 